1. Field of the Invention
The present invention relates to an accelerator pedal assembly applicable to a vehicle, etc., and more particularly relates to an accelerator pedal assembly applicable to vehicles adopting a drive by wire system.
2. Description of Related Art
Electronically controlled throttle systems such as drive-by-wire systems are well known as methods for performing fine control in a highly precise manner on the combustible state, output, and rotational control etc. of an engine mounted in a vehicle, particularly in an automobile. Rather than having an accelerator pedal and a throttle valve connected by an accelerator cable, such electronically controlled throttle systems (drive-by-wire systems) convert the extent to which an accelerator pedal is pressed down to an electrical signal, and output of the engine is controlled based on this converted electrical signal.
In such drive-by-wire systems, the operating load of the throttle valve does not act on the accelerator pedal as a pedal load. When the vehicle is then made to advance at a fixed speed (when the accelerator is held at a fixed position), a mechanism for supplementing this load, so that the driver does not become tired, is required. When vehicle acceleration fluctuates due to changes in engine output, etc., the driver is subjected to the influence of an oscillatory system, causing the pressing of the accelerator pedal to easily fluctuate, inviting vibration of the vehicle towards the front and rear. A mechanism is therefore required to generate a force resisting the pushing down of the accelerator pedal in order to prevent such vibration.
The mechanism disclosed in, for example, Japanese Patent Laid-open Publication No. Hei. 11-235936 is well known as an accelerator pedal assembly for dealing with this problem. The accelerator pedal assembly disclosed in this publication comprises a pedal arm capable of swinging from a rest position to a maximum depression position due to depression force from an accelerator pedal, a return spring causing the pedal arm to return towards the rest position, a moveable friction member made to move by the pedal arm, a returning spring for returning the moveable friction member to its original position, and a housing for guiding the moveable friction member in a freely sliding manner. A frictional force generating mechanism for generating a prescribed frictional force is therefore constituted by the moveable friction member and housing. According to this frictional force generating mechanism, a function is provided where a fixed frictional force acts in such a manner that a pedal load is exerted upon the accelerator pedal while the accelerator pedal is being depressed, while on the other hand, a fixed frictional force resisting the urging force of the return spring acts so as to reduce the returning force of the accelerator pedal when the accelerator pedal is returning. A desired position can therefore be maintained for the accelerator pedal when travelling at a fixed speed because a prescribed operating load (pedal load) is acting on the accelerator pedal and driver fatigue can be alleviated.
With the accelerator pedal apparatus equipped with the aforementioned frictional force generating mechanism, as shown in FIG. 8 and FIG. 9, the relationship between the depression force of the accelerator pedal (pedal load) and the amount of movement of the accelerator pedal (stroke) is that of hysteresis of a fixed width from the throttle being completely closed (commencement of depression of the accelerator pedal) to being completely open (position of maximum depression). Therefore, as shown in FIG. 8, if the depression force (pedal load) is aligned to that required on the completely open side of the throttle, the returning force is insufficient at the completely closed position and the accelerator response (accelerator feeling) deteriorates. On the other hand, as shown in FIG. 9, when the depression force (pedal load) is aligned to that required on the completely closed side, either the driver or the accelerator pedal will vibrate with respect to vibrations of the vehicle on the completely open side, and there is the possibility that driveability will deteriorate.
In order to resolve the aforementioned problems, it is the object of the present invention to provide an accelerator pedal assembly fulfilling a required hysteresis characteristic for depression force (operating load) required from the throttle being completely closed to being completely open, i.e. over the entire range of movement of the accelerator pedal, which has a straightforward structure, is small in size, and contributes to superior driveability.
The accelerator pedal assembly of the present invention comprises a pedal arm capable of moving from a rest position to a position of maximum depression as a result of depression force transmitted from an accelerator pedal. A pedal shaft supports the pedal arm in a freely sliding manner and a return spring urges the pedal arm back towards the rest position. A frictional force generating mechanism generates frictional force according to movement of the pedal arm, and comprises a sliding guide path defining a sliding surface for generating frictional force and a frictional force varying means located within the sliding guide path for varying frictional force according to movement of the pedal arm in such a manner that frictional force generated when the pedal arm moves towards the position of maximum depression increases according to the amount of movement, and frictional force generated when the pedal arm moves towards the rest position is reduced according to the amount of movement.
According to this configuration, the frictional force varying means increases frictional force generated within the sliding path according to the amount of movement when the accelerator pedal is being depressed so that the pedal arm moves from the rest position to the position of maximum depression so that a frictional force increasing according to the amount of depression of the accelerator pedal is added to the urging force of the return spring to act as the pedal load. On the other hand, the frictional force varying means reduces frictional force generated within the sliding guide path according to the amount of movement when the pedal arm is moving from the position of maximum depression to the rest position (returning) so that an urging force that is the urging force of the return spring, with a frictional force reduced according to the extent of returning of the accelerator pedal subtracted, acts as a pedal load. As a result, a pedal load characteristic is obtained wherein hysteresis has a minimum width at the rest position and a maximum width at the position of maximum depression.
The generated frictional force acts on the sliding surface of the sliding guide path and the direction of the reaction incurred by the pedal arm coincides with the direction of the action of the pedal arm on the frictional force generating mechanism (a direction opposing by 180 degrees). This means that structural parts such as the pedal shaft supporting the pedal arm are not subjected to excessive force and the reliability of operation is therefore increased.
The frictional force varying means has a configuration comprising a moveable friction member made to move within the sliding guide path by a load applied from the pedal arm. The moveable friction member is displaced in a direction orthogonal to the direction of movement in response to the load in such a manner as to push against the sliding surface. A returning spring generates an urging force for urging the moveable friction member in a direction resisting the load of the pedal arm, the moveable friction member being subject to displacement in a direction orthogonal to the direction of movement according to the urging force, the returning spring pushing the moveable friction member against the sliding surface so as to return the moveable friction member to the original position.
According to this configuration, when the moveable friction member moves towards the position of maximum depression due to the depression load of the pedal arm, the urging force of the returning spring also increases in response to the amount of movement. The pushing force with which the moveable friction member pushes against the sliding guide path (sliding surface), i.e. the frictional force, also increases according to the amount of movement. Further, when the moveable friction member moves towards the rest position due to the urging force of the returning spring, the urging force of the returning spring also becomes smaller in response to the amount of movement. The pushing force with which the moveable friction member pushes against the sliding guide path (sliding surface), i.e. the frictional force, therefore also decreases according to the amount of movement.
With the accelerator pedal assembly of the present invention, a configuration can be adopted where the frictional force varying means comprises a first moveable friction member moving within the sliding guide path due to the load of the pedal arm and having a first inclined surface forming a prescribed angle with respect to the direction of movement, a second moveable friction member, positioned opposite the first moveable friction member with respect to the direction of movement, moving within the sliding guide path and having a second inclined surface making contact with the first inclined surface, and a returning spring for urging the second moveable friction member in a direction opposing the load of the pedal arm so as to return the second moveable friction member to an original position.
According to this configuration, when the first moveable friction member and the second moveable friction member move towards the position of maximum depression due to the depression load of the pedal arm, the first moveable friction member and the second moveable friction member are pushed towards the sliding guide path by the wedging action of the first inclined surface and the second inclined surface. Frictional force therefore also increases according to the amount of depression (moving amount) because this pressing increases according to the amount of depression of the accelerator pedal, i.e. according to increases in the amount of compression (urging force) of the returning spring.
On the other hand, when the first moveable friction member and the second moveable friction member move towards the rest position due to the urging force of the returning spring, the amount of compression (urging force) of the returning spring is also reduced according to the amount of returning movement (amount of movement). The pushing force with which the first moveable friction member and the second moveable friction member are pushed along the sliding guide path, i.e. the frictional force, is also reduced according to this returning amount (amount of movement).
In the above configuration, a configuration can be adopted where a play load spring, generating a smaller urging force than the urging force of the returning spring, is located between the first moveable friction member and the second moveable friction member in a direction mutually avoiding the first moveable friction member and the second moveable friction member.
Accordingly, in a region from the rest position starting towards the position of maximum depression, it is possible to appropriately set a play region where the throttle valve does not operate even when depression force from the accelerator pedal acts on the pedal arm or to appropriately set a load characteristic to give a desirable feeling during operation.
An alternative configuration can be adopted wherein the play load is provided by an initial compression region of the return spring, instead of a separate play load spring.
In the above configuration, the returning spring may comprise a plurality of coil springs of different diameters. According to this configuration, the degree of freedom when setting urging force due to the returning spring can be increased, which contributes to making the assembly smaller. In the above alternative configuration of the play load, if the returning spring comprises a plurality of coil springs, one of such plurality of coil springs may be used to provide the play load. With the above configuration, the free end of the pedal arm can be arranged to freely engage with and release from the first moveable friction member. Accordingly, when the pedal arm is returning towards the rest position, the pedal arm is reliably returned to the rest position even if the first moveable friction member or the second contacting member become stuck and cannot return to the original position.